1. Field of the Invention
This invention relates to a multi-piece solid golf ball which has superior flying performance, feel on impact and durability and lends itself to mass production.
2. Prior Art
Two-piece solid golf balls are widely used because of the advantage that the amateur golfer can gain increased flying distance. These balls, however, have the disadvantages of an increased run, difficult control and hard hitting feel. The hitting feel can be mitigated by reducing compression at the sacrifice of repulsion and flying distance.
One solution to this problem is a multi-piece solid golf ball wherein the ball structure, especially the solid core section is divided into two, three or more layers having varying hardness, specific gravity and radial thickness (or radius). The conventional multi-piece solid golf balls, however, still leave some problems associated with their manufacture and are not suitable for mass production. By way of illustration, an exemplary three-piece solid golf ball has a two-layer core circumscribed by a cover. The two-layer solid core includes inner and outer layers, both being formed of rubber compositions based on polybutadiene rubber and containing a metal salt of an unsaturated carboxylic acid, a peroxide and the like. The solid core is prepared from these rubber compositions by first forming the core inner layer by a heating, pressing and shaping procedure in a manner as used to form the core of two-piece solid golf balls. The core inner layer is then covered with the core outer layer by first preforming the outer layer composition into a half shell shape in unvulcanized or semi-vulcanized state, and fitting the half shells over the core inner layer followed by a heating, pressing and shaping procedure again. Undesirably, this core preparation process requires more than twice the number of steps required for the preparation of the core of conventional two-piece solid golf balls.
It might be possible, but is impractical to mold and cure the core outer layer rubber composition by an injection molding technique. As is well known in the art, rubber as typified by polybutadiene has many problems against molding that it is poor in flow and requires a long cycle time since curing reaction must be incurred during molding.
Another three-piece golf ball is proposed in Japanese Patent Application Kokai (JP-A) No. 244174/1992 or GB 9117871 and 2248067 as comprising an elastomeric core, an intermediate layer, and a cover of thermoplastic material, the intermediate layer being formed of a thermoplastic composition containing at least 10% by weight, preferably at least 35% by weight of an amide block copolymer based on the total weight of the composition.
There is a need for a multi-piece solid golf ball which is further improved in performance and simplified in manufacturing steps.